Methods of fabricating binding layers for a Li-ion polymer battery

ABSTRACT

A Li-ion polymer battery and methods for its fabrication. A first and second layer, of a polymer/particulate material composition, separate and bind each anode and cathode. The polymer of the first layer and its associated solvent differ from the polymer of the second layer and its associated solvent. Solubility requirements are such that the polymer of the first layer is non-soluble in the solvent of the second layer, and the polymer of the second layer is non-soluble in the solvent of the first layer. The polymers and particulate materials of the layers form a porous structure for containing the electrolyte of the battery so as to eliminate the need for a substantial case for enclosing the battery.

FIELD OF THE INVENTION

The present invention relates to a lithium-ion secondary battery whereinanodes and cathodes are separated and bound by two different porouslayers of polymeric materials containing particulate matter, and methodsfor fabricating the same.

BACKGROUND OF THE INVENTION

Lithium-ion polymer batteries are fabricated by various methods. In U.S.Pat. No. 5,536,278 an electrolyte film, previously prepared, is heatedand laminated to a first electrode. The second electrode is thenlaminated to the laminated first electrode.

In U.S. Pat. No. 5,778,515 an electrode film and a separator film areformed then laminated after use of a pre-lamination solvent on thesurface at least one of the films.

In U.S. Pat. No. 6,024,773 a separator film is coated on both sides witha binder resin solution so as to bond the electrodes with the separatorfilm separating them.

In U.S. Pat. No. 5,348,824 polymer based amorphous compositions are meltextruded in the form of a thin film directly on the positive electrodeof a lithium battery.

In all of the processes in which a sheet or film is formed, thecomposition of the separator material is limited to polymers havingsatisfactory mechanical strength for forming a thin film and forcarrying out the laminating process with the electrodes. Use ofparticulate material in the polymer, to any great extent, is nearlyimpossible with any polymer as the mechanical strength is decreasedfurther with the addition of the particulate material. In melt extendedpolymers, the porosity is difficult to control and is typically low.

Those disadvantages and other are overcome with use of the presentinvention.

SUMMARY OF THE INVENTION

The present invention is concerned with a Li-ion polymer battery andmethods for its fabrication. Two layers of differing polymeric materialsare provided, in non-sheet form, to separate and bind adjacent anodesand cathodes (electrodes) of the battery. The Layers contain aparticulate material to increase porosity of the layers. The differingpolymeric materials have specific solubility requirements which aredescribed below.

The battery has at least one anode and at least one cathode which is inopposing spaced relationship to each anode. Two layers of differingporous separators/binders are intermediate each anode and cathode tomaintain the spacing and to bind each anode to each cathode. Anon-aqueous electrolyte fills the pores of the separators/binders. Eachseparator/binder consists of a polymer and particulate material. A firstseparator/binder is made up of polymer P₁ and particulate material M₁;the second separator/binder is made up of polymer P₂ and particulatematerial M₂. The polymers and particulate materials must have solubilityproperties such that P₁ is soluble in solvent S₁, P₂ is soluble insolvent S₂, P₁ is non-soluble in solvent S₂, P₂ is non-soluble insolvent S₁, M₁ is non-soluble in S₁, and M₂ is non-soluble in S₂.

Preferred structures of the batteries are a prismatic form (stacked) anda cylindrical form (wound). Fabrication is carried out by threefabricating methods. In all of the methods the first separator/binder,in which the polymer is dissolved in a solvent, is applied to theelectrodes in such a manner that a single layer of the firstseparator/binder will be present between each anode and cathode in thecompleted battery. The first separator/binder is then dried. The secondseparator/binder is provided in differing manners in each of the threemethods, however the polymer of the second separator/binder is in atleast a partially dissolved condition while the electrodes are in astacked form in order that the electrodes are bound in either theprismatic or cylindrical form when the second separator/binder is driedby evaporation of the solvent S₂.

In a first method the electrodes are stacked while the secondseparator/binder is not fully dried and in a tacky condition.

In a second method the electrodes are stacked with only the firstseparator/binder between them and the second separator/binder isinfiltrated to between the electrodes and then dried.

In a third method the electrodes are stacked with a first and a secondseparator/binder, in a dried condition, between them; solvent S₂ is theninfiltrated to between the electrodes so as to at least partiallydissolve polymer P₂ such that when dried the electrodes will be boundtogether.

Final fabrication of the batteries, in all three methods, includesproviding a non-aqueous electrolyte to fill the pores of theseparators/binders and packaging the electrodes and electrolyte.

BRIEF DESCRIPTION OF THE DRAWING

In order that the invention may be more readily understood, reference ismade to the accompanying drawings in which:

FIG. 1 is a vertical section of a portion of a battery of the inventionshowing the alternating anodes and cathodes and the intermediate layersof separator/binder, the battery having a prismatic structure;

FIG. 2 is a schematic drawing of a battery of the invention, the batteryhaving a cylindrical structure;

FIGS. 3a, 3 b, 3 c are drawings for describing fabricating steps carriedout for the first method of fabrication of the invention for a prismaticbattery;

FIGS. 4a, 4 b, 4 c are drawings for describing alternative fabricatingsteps to steps shown in FIGS. 3a-3 c carried out for the first method offabrication of the invention for a prismatic battery;

FIGS. 5a, 5 b, 5 c, 5 d and 5 e are drawings for describing fabricatingsteps carried out for the second method of fabrication of the inventionfor a prismatic battery;

FIGS. 6a, 6 b, 6 c and 6 d are drawings for describing alternativefabricating steps to steps shown in FIGS. 5a-5 e carried out for thesecond method of fabrication of the invention for a prismatic battery;

FIGS. 7a, 7 b, 7 c, 7 d and 7 e are drawings for describing fabricatingsteps carried out for the third method of fabrication of the inventionfor a prismatic battery;

FIGS. 8a, 8 b, 8 c, 8 d and 8 e are drawings for describing alternativefabricating steps to steps shown in FIGS. 7a-7 e carried out for thethird method of fabrication of the invention for a prismatic battery;

FIG. 9 is a schematic drawing of completely fabricated battery of theinvention;

FIGS. 10a, 10 b and 10 c are drawings for describing fabricating stepscarried out for a first method of fabrication of the invention for acylindrical battery;

FIG. 11 is a drawing for describing fabricating steps carried out for asecond method of fabrication of the invention for a cylindrical battery;

FIGS. 12a, 12 b and 12 c are drawings for describing fabricating stepscarried out for a third method of fabrication of the invention for acylindrical battery;

FIG. 13 is a graph for showing a first set of testing conditions carriedout on a prismatic battery of the invention fabricated by method 1;

FIG. 14 is a graph for showing the results of the test carried out usingthe conditions shown in FIG. 13;

FIG. 15 is a graph for showing a second set of testing conditionsdifferent from the set of FIG. 13 carried out on the same prismaticbattery of the invention fabricated by method 1;

FIG. 16 is a graph for showing the results of the test carried out usingthe conditions shown in FIG. 15;

FIGS. 17-24 are graphs for showing a third set of testing conditions andcorresponding results, for a prismatic battery fabricated by the firstmethod, but using a differing separator/binder than that of the batteryof FIGS. 13-16;

FIG. 25 is a graph for showing a fourth set of testing conditionscarried out on a battery of the invention fabricated by method 1, butusing differing separators/binders then previous method 1 examples;

FIG. 26 is a graph for showing the results of the test carried out usingthe conditions shown in FIG. 25;

FIG. 27 is a graph for showing a fifth set of testing steps carried outon a wound type battery of the invention fabricated by method 2;

FIG. 28 is a graph for showing the results of the test carried out usingthe conditions shown in FIG. 27;

FIG. 29 is a graph for showing the results of a sixth test carried outon a cylindrical (wound) battery of the invention fabricated by method3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The battery of the present invention is a rechargeable battery having atleast one anode and one cathode (electrodes) in spaced relationship anda liquid electrolyte disposed in the space between them in order thations can pass freely between the anode and the cathode. To be ofpractical use, the battery of a prismatic form consists of a pluralityof anodes and cathodes, in spaced relationship, with the liquidelectrolyte occupying each space. Two possible configurations for Li-ionbatteries are described: 1) a battery having substantially flat anodesand cathodes stacked in an alternating arrangement, referred to as“prismatic” battery, and 2) a battery having a single elongated anodeand a single elongated cathode stacked and then wound in a coil fashion,usually about a core, referred to generally as “cylindrical” battery.

In order to maintain the spaced relationship and avoid contact and ashort circuit between the anodes and the cathodes, and, in order to bindthe anodes and the cathodes into a structure requiring no external meansfor support, two layers of separator/binder, configured to have a highlevel of porosity, are provided between each anode and cathode. Both ofthe layers act as separators and as binders and contain the electrolytein their pores.

Referring to FIG. 1, an example of the prismatic arrangement, anodes 30are stacked in an alternating manner with cathodes 32. The cathodes canconsist of any known cathode structure, for example an aluminum foilhaving formed on its surfaces a positive electrode active material layersuch as complex oxides of lithium such as LiCoO₂. Other active materiallayers can consist of lithiated manganese oxide, lithiated nickel oxide,and combinations thereof. The anode can consist of any known anodestructure, for example a copper foil having formed on its surfaces acarbonaceous material such as carbonaceous graphite. Other examples ofelectrodes include metallic lithium, lithium, lithium alloys, aluminum,and lithium intercalation materials such as carbon, petroleum coke,activated carbon, graphite, and other forms of carbon known in the art.Other substrate foils can consist of gold, nickel, copper alloys, andcopper plated materials.

A first separator/binder layer 34 and a second separator/binder layer36, made up of particulate materials and polymers P₁ and P₂respectively, fill the space between the anodes and cathodes.

In FIG. 2, a cylindrically shaped arrangement of an anode and a cathodeis shown having anode 38, cathode 40 and two separator/binder layers 34a and 36 a in the space between the anode and cathode. The anode andcathode material can be similar to those described for the prismaticarrangement.

Referring to FIG. 1, intermediate each anode and cathode are two layersof separators/binders, 34 and 36 which maintain a separation betweeneach anode and cathode and act as a binder to hold the anodes andcathodes in position. No means external ton the electrodes are necessaryto maintain the structure of the battery The separators/binders areapplied to the electrodes as a liquid and the method of application isdescribed below. The liquid separators/binders are prepared bydissolving polymers in a solvent to obtain a polymeric solution followedby adding a particulate material to the solution. For example, PVC(polyvinylchloride) is dissolved in THF (tetrahydrofuran). If polymer P₁is dissolved in solvent S₁, and polymer P₂ is dissolved in solvent S₂, arequirement of the invention is that P₁ is soluble in S₁ and non-solublein S₂; and that P₂ is soluble in S₂ and non-soluble in S₁. For example,P₁ could be PVC; S₁ could be THF; PZ could be PEO (polyethylene oxide);and S₂ could be methanol. The polymeric materials can be roughlycategorized as hydrophilic and hydrophobic. The following tables presentpossible combinations that can be used which follow the aboverequirements. The tables do not include all possible combinations. Anyhydrophilic polymeric material from Table I can be used with anyhydrophobic polymeric material from Table II.

TABLE I (Hydrophilic) POLYMER SOLVENT PEO (polyethylene oxide) methanolPPO (polypropylene oxide) methanol polycarbonate methanol/chloroformPMMA (polymethyl methacrylate) ethanol PVP (polyvinyl pyrrolidone)methanol

TABLE II (Hydrophobic) POLYMER PE/PP (polyethylene/polypropylene)heptane PVC (polyvinylchloride) tetrahydrofuran polystyrenetetrahydrofuran PAN (polyacrylonitrile) DMF (dimethyl sulfoxide) PAN(polyacrylonitrile) DMSO (dimethyl sulfoxide)

It is also possible to select polymer/solvent combinations for both thefirst and second separator/binder layers from within either Table I orTable II and still comply with the solubility requirements stated above.

As discussed above, for a Li-ion battery to operate, it is necessarythat an electrolyte be present in the separation between the electrodesin order that ions can move freely between the electrodes. In order toprovide porosity in each separator/binder a particulate material isadded to the dissolved polymer prior to its application to theelectrodes. A preferred particulate material is borosilicate glassfibers. Other materials can include particulate materials such as: oxideparticles such as magnesium oxide, calcium oxide, strontium oxide,barium oxide, boron oxide, aluminum oxide, silicon oxide; synthetic ornatural zeolites; silicates such as borosilicate, calcium silicate,aluminum polysilicates; cellulosic materials such as wood flours, andglass materials such as microbeads, hollow microspheres, flakes; orparticulate materials in the fiber form such as: polyester fibers, nylonfibers, rayon fibers, acetate fibers, acrylic fibers, polyethylenefibers, polypropylene fibers, polyamide fibers, polybenzimidazolefibers, borosilicate glass fibers, and-wood fibers.

An example of a liquid separator/binder for application to an electrodeis: 0.5 gm of PVC dissolved in 20 gm of THF to which 9.5 gm of,borosilicate is added. In a preferred embodiment the borosilicate isprepared as glass fibers which have been processed in a ball mill forapproximately 24 hours. After the ball mill processing the fibers are ina powder form.

A second example of a liquid separator/binder for application to anelectrode is: 1 gm of PEO dissolved in 30 gm of methanol with 5 gm ofborosilicate added.

A separator/binder, prepared as indicated above, upon being applied tothe electrode and dried, produces a porous layer wherein the particulatematerial is coated with the polymer and bound-to the surface of theelectrode. The solvent of the applied material is substantiallycompletely evaporated in the drying process leaving voids between thepolymer-coated particles as the polymer shrinks back as the solventevaporates. In a subsequent fabricating step a liquid electrolyte isprovided which fills the voids of each separator/binder layer betweenthe electrodes.

FIGS. 3a through 12 c show various steps for three different methods offabricating Li-ion batteries of the invention. Prismatic type batteriesare described first, followed by cylindrically structured batteries.

In a first step of the first method, FIG. 3a, anode 30 is coated on oneside with a first separator/binder 34 and dried. A preferred method ofcoating which applies to all the following examples is to prepare theseparator/binder by combining the polymer, the solvent, and theparticulate material and continually stirring the mixture for a periodof about 8 to 12 hours. The stirring is carried out until the polymerand the particulate material in suspension is homogeneous. The length oftime for stirring is dependent upon the polymer type and the particulatematerial. Following preparation of the separator/binder, a bar coatingprocess, using a metallic net to control thickness, is carried out. Thethickness of the coating is controlled to be between 10 and 200 μm.Preferably, the thickness is controlled to be between 30 and 60 μm. Withthe use of metallic nets of differing thickness the coating thicknesscan be regulated. However, other methods resulting in a similar uniformcoating can be used. In the present first method of fabricating,following coating of the first separator/binder, 34, drying is carriedoust to evaporate the solvent. Complete drying however is not necessaryat this stage of fabrication.

In a second step of the first method, FIG. 3b, the cathode 32 is coatedwith a second separator/binder 36 prepared in the same manner asdiscussed above. However, this coating is not completely dried. Whilethe second separator/binder, 36, is still at least tacky on cathode 32,the anode 30, having the dried coating of the first separator/binder,34, is layered with the cathode 32 as shown in FIG. 3c so as to bind thestack of electrodes. The process is repeated to obtain the number oflayers desired.

The polymers P₁ and P₂ of the first and second separator/binderrespectively (FIGS. 3a-3 c) have the solubility restrictions discussedabove. Since polymer P₁ is not soluble in the solvent S₂ of polymer P₂₂,polymer P₁ is not dissolved when placed in contact with the liquid (atleast tacky) polymer P₂ in the step shown in FIG. 3c. As a result P₁remains solid in the uniform layer as applied and thus guarantees theseparation between the electrodes. Additionally the layer of the secondseparator/binder, 36, containing polymer P₂ adds to the separationbetween the electrodes. As can be seen in FIG. 3c anode 30 is bound tothe first separator/binder layer 34, the first separator/binder layer 34is bound to the second separator/binder layer 36, and the secondseparator/binder layer 36 is bound to cathode 32. No additional supportmeans is required to maintain the structure of the battery. Additionalalternating anodes and cathodes can be added in a similar manner toproduce a battery of a selected size and capacity. After assembling thedesired number of electrodes, the assembly is preferably dried under avacuum at 120° C. for 8 hours. The coatings applied to each electrodecover the area necessary to be opposed by the adjacent electrode. Theuncoated portions of the electrodes extend from sides of the stack, asshown in FIG. 1, and are connected electrically in subsequent steps ofthe assembly as is known in the art.

The specific sequence of coating and relative arrangement of the twoseparator/binder layers as shown in FIGS. 3a-3 c is not unique. Anyprocedure resulting in a first separator/binder layer and a secondseparator/binder layer between each anode and cathode is acceptable.However, during assembly the first separator/binder layer must beapplied and dried and the second layer must be at least tacky whenstacking takes place. An alternate first method of fabrication is shownin FIGS. 4a to 4 c. In FIG. 4a two anodes 30 are coated with the firstseparator/binder 34 on both sides and dried. In FIG. 4b one cathode 32is coated with the second separator/binder layer 36. In the final step,FIG. 4c, the anodes 30 and cathode 32 are stacked while the secondseparator/binder 36 is at least still tacky. Additional layers can beadded in a similar manner.

Steps described above, (FIGS. 3a-3 c), along with subsequent steps tocomplete fabrication of the battery include:

1) coating one side of one electrode (e.g. anode) with the firstseparator/binder layer 34

2) drying the first layer 34

3) coating one side of one opposite electrode (e.g. cathode) with thesecond separator/binder layer 36

4) stacking the electrodes while the second layer, 36, is still at leasttacky

5) adding additional anodes and cathodes in a similar manner for aselected number of electrodes

6) drying the completed stack of electrodes

7) providing the desired electrical connections to the electrodes

8) infiltrating an electrolyte to the pores of the two separator/binderlayers of the stack of electrodes

9. placing the stacked electrodes into a suitable container and sealingthe container

In order to prevent moisture from being present within the sealedcontainer, steps 8 and 9 are preferably carried out in a dry room.Electrolytes, discussed below, are non-aqueous, and the presence ofmoisture is detrimental to the operation of the battery.

In the above examples and following examples, the percent of particulatematerial in the first separator/binder (by weight) is in the range of50-98%; the percent of particulate material in the secondseparator/binder (by weight) is in the range of 50-98%. The preferredpercent for the first separator/binder is in the range of 80-97%. Thepreferred percent for the second separator/binder is in the range of70-92%.

A second method of fabricating a battery of the invention is presentedin FIGS. 5a through 5 e. In a first step of the second method, FIG. 5a,anode 30 is coated with the first separator/binder, 34, and dried. Instep 2, FIG. 5b, cathode 32 is coated with the first separator/binder 34and dried. Steps 1 and 2 are repeated for a selected number of anodesand cathodes. In step 3, FIG. 5c, the prepared anodes and cathodes areloosely stacked in a manner such that a single layer of the firstseparator/binder, 34, is present between each alternating anode 30 andcathode 32. In step 4, FIG. 5d, the second separator/binder, 36, isinfiltrated to spaces between the dried layers 34 and opposed uncoatedelectrode surfaces. The step can be carried out by immersion in theliquid or by any other means. FIG. 5e shows the completed assemblyhaving alternating anodes 30 and cathodes 32 with a layer of eachseparator/binders 34 and 36 between them. The requirements of polymersP₁ and P₂ of first and second separator/binders 34 and 36, stated above,are especially important in the present method in order that the driedfirst layer with polymer P₁ remains undissolved and maintained at theuniform thickness which was applied in steps 5 a and 5 b.

FIGS. 6a-6 d show an alternative manner of fabrication using the secondmethod. In FIG. 6a anode 30 is coated with the first separator/binder 34on both sides and dried. A plurality of additional anodes are likewiseprepared. In a second step, FIG. 6b, the prepared anodes are looselystacked, in an alternating manner with non-coated cathodes. In a thirdstep, FIG. 6c, the loosely stacked electrodes are infiltrated with thesecond separator/binder so as to add a second separator/binder layer 36between each dried first separator/binder layer 34 and the non-coatedsurface of cathode 32 as shown in FIG. 6d. This same process can beused, for example, by coating cathodes and stacking them with non-coatedanodes.

Steps described above (FIGS. 6a-6 d), along with subsequent steps tocomplete fabrication of the battery include:

1) coating both sides of electrodes (e.g. anodes) with the firstseparator/binder layer 34

2) drying the first layer 34

3) loosely stacking the coated electrodes in an alternating manner withnon-coated electrodes (e.g. cathodes)

4) infiltrating the loosely stacked electrodes with the secondseparator/binder 36

5) drying the stack of electrodes

6) providing the desired electrical connections to the electrodes

7) infiltrating an electrolyte to the pores of the two layers of thestack of electrodes

8) placing the stacked electrodes into a suitable container and sealingthe container Steps 7 and 8 are preferably carried out in a dry room.

A third method of fabricating a battery of the invention is presented inFIGS. 7a-7 e. In FIG. 7a anode 30 is coated on both sides with the firstseparator/binder 34 and dried. In a second step, FIG. 7b, cathode 32 iscoated on both sides with the second separator/binder 36 and dried. Theanodes and cathodes are then stacked in an alternating manner as shownin FIG. 7c. In a next step the stacked electrodes are infiltrated withthe solvent S₂ of the second separator/binder 36 by immersion of thestack in solvent S₂ so as to dissolve at least a portion of the polymerP₂ as shown in FIG. 7d. In a final step, FIG. 7e, the stacked electrodesare dried so as to bind the electrodes together. The completed stack ofelectrodes have a layer of the first separator/binder and a layer of thesecond separator/binder between each anode and cathode.

FIGS. 8a-8 e show an alternate manner of fabrication using the thirdmethod. In FIG. 8a anode 30 is coated on both sides with the firstseparator/binder 34 and dried. Then, the second separator/binder 36 isapplied on top of the first separator/binder and dried.

FIG. 8b shows cathode 32 which is free of any coating of aseparator/binder. In FIG. 8c a plurality of coated anodes and non-coatedcathodes are stacked in an alternating manner. In a next step, FIG. 8d,the stacked electrodes are emersed in solvent S₂ so as to dissolve atleast a portion of the second separator/binder 36. And, in a final step,FIG. 8e, the assembly is dried thereby bonding each anode to eachcathode.

Steps of FIGS. 7a-7 e along with subsequent steps to complete thefabrication of the battery include:

1) coating both sides of an electrode (e.g. anode) with the firstseparator/binder 34

2) coating both sides of an unlike electrode (e.g. cathode) with thesecond separator/binder 36

3) repeating steps 1 and 2 for a plurality of anodes 30 and cathodes 32

4) stacking a plurality of coated electrodes

5) infiltrating solvent S₂ of polymer P₂

6) drying the stack of electrodes

7) providing the desired electrical connections to the electrodes

8) infiltrating an electrolyte to the pores of the two layers of thestacked electrodes

9) placing the stacked electrodes into a suitable container and sealingthe container

Steps 8 and 9 are preferably carried out in a dry room.

Although it is shown to apply the second separator/binder on top of thefirst separator/binder only in the third method of fabrication, asimilar procedure can also be carried out with the first method. In thefirst method, the second separator/binder is not completely dried priorto performance of the next step.

A fully fabricated battery of the invention is shown schematically inFIG. 9. Stacked anodes, 30, and cathodes, 32, have one layer ofseparator/binder 34 and one layer of separator/binder 36 between eachelectrode. The stacked electrodes and layers of separator/binder can beprepared by any of the methods describes above as all of the methodsresult in substantially the same battery. An electrolyte, 42, fills thepores of all of the layers of separator/binder between the electrodes.Conductors 44 and 46 connect all of the anodes and cathodes,respectively, and extend out of sealed container 48 as electrical leadsat 50 and 52. Various means for connecting the anodes and cathodes areknown in the art. One method of connecting the electrodes (not shown) isto spot-weld a nickel mesh to the electrode ends which extend from theelectrode stack.

Various containers are known in the art. One example of a container isan aluminum foil bag, laminated, at least on an internal surface, with apolymer such as PE or PP.

As discussed above, a battery of the invention can have a cylindrical(wound) structure. A cylindrical or hexahedron shaped core is preferredfor winding the coated electrodes about. The three methods offabrication described for prismatic batteries can be used to fabricatecylindrical batteries. One example of each of the methods is describedbelow. One skilled in the art can devise alternative variations toachieve the same results.

In FIG. 10a an elongated anode 30 a is coated on both sides with thefirst separator/binder 34 and dried. Elongated cathode 32 a is coated onboth sides with the second separator/binder 36, FIG. 10b. While thesecond separator/binder 36 is still at least tacky the coated anode andcathode are rolled about a core in coil form as shown in FIG. 2 anddried. The dried cylindrically shaped battery is bound in that shape bythe two separator/binder layers without any additional structure.

In the second method of fabricating a cylindrical battery of theinvention, described with reference to FIG. 11, the battery isfabricated by coating an elongated anode, 30 a, on both sides with thefirst separator/binder 34 and dried. In a second step the coatedelongated anode is rolled with an elongated non-coated cathode about acore. A separation between the first separator/binder 34 and thenon-coated surface of the elongated cathode is infiltrated with thesecond separator/binder 36 such as by immersion. In a final step, thecoiled anode and cathode are dried to bind each anode to each cathode asin FIG. 2.

A third method of fabricating a cylindrical battery of the invention isdescribed with reference to FIGS. 12a-12 c. In FIG. 12a, an elongatedanode 30 a is coated on both sides with the first separator/binder 34and dried. In a second step, FIG. 12b, elongated cathode 32 a is coatedon both sides with the second separator/binder 36 and dried. The coatedelongated anode and cathode are stacked and rolled about a core in coilform. The rolled electrodes are infiltrated, such as by immersion, withthe solvent S₂ of polymer P₂ so as to dissolve at least a surfaceportion of the polymer P₂ without any effect on the firstseparator/binder 34 layer having polymer P₂₁. FIG. 2 shows the completedstructure having a continuous anode 30 a and a continuous cathode 32 bwith one layer of separator/binder 34 and one layer of separator/binder36 between them. The structure is bound in the coil shape by the driedpolymers without any external structure. Other procedures for producingcylindrical batteries using the three general methods of fabrication arealso possible.

Lithium-ion batteries fabricated with use of the above three methodshave numerous advantages over batteries fabricated by known methods suchas using a continuous film or sheet formed of a polymer. Examples of theadvantages of the present invention are:

1) Many different polymers can be used for the separating and bindinglayers without consideration of their mechanical properties. Inbatteries fabricated using a continuous film formed of a polymer onlycertain polymers having certain mechanical properties can be used.

2) Previous concerns for “pin holes” in a continuous polymeric film isnot a concern with the present method. Even if a “pin hole” would bepresent in one of the layers, the second layer would prevent physicalcontact of the anode and cathode.

3) The batteries of the present invention require no external structureto hold the electrodes in position. The layers of polymeric materialbind the electrodes. As a result, no steel case is required whichincreases the thickness and weight of the resultant battery.

4) The separator/binder layers can be very thin, since mechanicalstrength and pin hole problems are not the concern, thereby a very thinbattery can be constructed.

5) Most of the fabrication can take place outside a dry room. Polymerfilms for battery fabrication of the prior art are usually handled in adry room so as to prevent the absorption of moisture in the film, whichis difficult to remove after fabrication. In the present invention onlythe final steps are carried out in a dry room.

6) In comparison with batteries having a polymer film in sheet form withlayers of polymers on each face provided for binding between the filmand each electrode, the present battery has one less interface betweenpolymeric material layers. Imperfect interfaces can result in anincrease of electrical resistance.

7) Since the layers of separator/binder fill substantially the entirespace between the electrodes, the liquid electrolyte is absorbed in asponge-like manner and is substantially contained, thus no extra liquidelectrolyte is required.

8) The present method can be used on any known electrode materials.

9) Since the two separator/binder layers are intimately bound to theelectrode surfaces, excellent wetability of the electrode surfaces isachieved.

10) The battery is a solid bound structure with substantially no voidsintermediate the anodes and cathodes.

11) The binding effect is better with the two separator/binder layerscompared with binding carried out on the surface of the conventionalsheet separator film.

Experimental testing was carried out on batteries fabricated by thethree methods of fabrication of the invention. Testing conditions andexperimental results are shown graphically in FIGS. 13 to 29.

In all of the experiments having a prismatic form, the foil of thecathodes had a dimension of 4 cm.×3.8 cm. with an active cathodematerial on each foil surface covering an area 3 cm.×3.8 cm. The foil ofthe anodes had a dimension of 4 cm.×4 cm. with an active anode materialon each foil surface covering an area 3 cm.×4 cm.

Also in all of the experiments the cathode foil was aluminum coated witha cathode active material of LiCoO₂. It should be noted that othercathode materials are possible. The anode foil was copper coated with ananode active material of carbonaceous graphite, similarly, other anodematerials are possible.

Example 1 was carried out using a battery fabricated by the first methodof fabrication. The first separator/binder was prepared by dissolving0.5 gm of PVC in 20 gm of THF, and then adding 9.5 gm of glass particlesprepared as described above and stirred until the desired homogeneity,described above, was obtained. The second separator/binder was preparedby dissolving 1 gm of PEO in 30 gm of methanol, and then adding 5 gm ofthe glass particles. The mixture was stirred to the same desiredhomogeneity.

The first separator/binder was applied to both sides of the cathodes,using the bar coating process, to a thickness of about 50 μm and driedby evaporating the THF. The second separator/binder was then applied toboth sides of the anodes, using the bar coating process, to a thicknessof about 50 μm. Prior to the complete evaporation of the solventmethanol the anodes and cathodes were stacked as shown in FIG. 1. Theelectrode stack consisted of 11 cathodes and 10 anodes. A nickel meshwas spot welded on the extending anode side and on the extending cathodeside to serve as current collectors for the resultant battery. Theelectrode stack was dried under vacuum at 120° C. for 8 hours and thenpacked in a polymer-laminated aluminum foil bag. A liquid electrolyte,(1M LiPF₆ in EC/DMC wt ratio 1:1) was added to the battery pack and thepack sealed. The electrolyte component EC/DMC is ethylenecarbonate/dimethyl carbonate. The resultant battery was then pressedwith one-ton pressure for 10 minutes just prior to testing. The steps ofadding the electrolyte and sealing the pack were carried out in a dryroom.

The experimental testing to determine discharge capacity was carried outas follows and is depicted graphically in FIG. 13:

1) The battery was charged and then discharged at a current of 0.15A fora first cycle, then charged and discharged for 10 cycles. Chargingconditions were 0.3A constant charge to 4.2V, then constant voltagecharge at 4.2V until the current <0.15A. Discharging conditions were0.3A constant discharge until the voltage=2.8V. The current of 0.3Aresults in a full charge or full discharge being carried out in about 2hours. A charging/discharging rate of such is referred to as a C-rateoff. C/2. In FIG. 13, the first charge/discharge cycle is not shown.Current (amps) is indicated by the line C and voltage (volts) isindicated by the line V. The horizontal axis indicates test timeexpressed in seconds. The results of the discharge capacity test areshown in FIG. 14. The horizontal axis indicates the cycle number and thevertical axis indicates the discharge capacity expressed in mAh. Adischarge capacity of about 550 mAh resulted for each of the cycles.

In example 2, a second discharge capacity test was carried out on thesame battery as example 1 using a different C-rate for discharging. Thetesting conditions are depicted graphically in FIG. 15. 10charging/discharging cycles were carried out at a discharge C-rate ofC/1, that is a current of 0.5A, and a charging C-rate of C/2, that is acurrent of 0.3A. As in graph 13, current (amps) is indicated by the lineC and voltage (volts) is indicated by line V. The horizontal axisindicates time in seconds.

The results of the discharge capacity test are shown in FIG. 16. Adischarge capacity of about 520 mAh resulted for each of the cycles. Thecycles are indicated as cycles 11 through 20 as the second test wascarried out on the same battery as the first test.

In example 3, a third discharge capacity test was carried out using abattery fabricated by the first method of fabrication. All of thefabricating steps were the same as Example 1 except the polymer P₁ wasprepared by dissolving 0.5 gm of copolymer PE/PP (PE content about 60%)in 20 gm of Heptane, then mixing in 9.5 gm of the glass particlesdescribed above. The following testing conditions, table III, werecarried out.

TABLE III Discharging Test Cycle Charging Conditions Conditions A  1-10300 mA constant charge to 4.2 V 300 mA constant then constant voltage of4.2 V discharge until until current < .15 A voltage was 2.8 V B 11-20300 mA constant charge to 4.2 V 500 mA constant then constant voltage of4.2 V discharge until until current < .15 A voltage 2.8 V C 21-30 300 mAconstant charge to 4.2 V 700 mA constant then constant voltage of 4.2 Vdischarge until until current < .15 A voltage 2.8 V D 31-60 300 mAconstant charge to 4.2 V 1 A constant then constant voltage of 4.2 Vdischarge until until current < .15 A voltage 2.8 V

The test conditions are depicted graphically, and the dischargecapacities for tests A, B, C and D are indicated graphically in FIGS.17-24. In FIGS. 17, 19, 21 and 23 current (amps) is indicated by theline C, and voltage (volts) is indicated by the line V. The variousresults can be seen in FIGS. 18, 20, 22 and 24.

In a fourth example, the battery was fabricated by the first method offabrication. All of the fabrication steps were the same as example 1except the number of electrode layers and the polymers were different.The test battery consisted of five cathodes and four anodes. The firstseparator/binder was prepared by dissolving 0.5 gm of polystyrene in 20gm of THF (tetrahydrofuran) then adding 5 gm of ball milled borosilicatefibers. The second separator/binder was prepared by dissolving 1 gm ofPVP in 20 gm of methanol then adding 9.5 gm of ball milled borosilicatefibers.

Testing conditions are depicted graphically in FIG. 25. The battery wasfirst charged and discharged at a current of 0.07 amps. After the firstcycle the battery was charged at a current of 0.2 amp (approximately C/1in C-rate) with a constant voltage charge of 4.2V, and a dischargecurrent of 0.2 amp.

The results of 5 cycles of the test are shown graphically in FIG. 26.

In a fifth example, the battery consisted of one anode and one cathodewound about a hexahedron shaped core and fabricated by the second methodof fabrication. The cathode dimensions were 3.8 cm.×25.2 cm. with anactive material coating of 3.8 cm.×24.2 cm. on one side and 3.8 cm.×18.2cm. on the other side. The anode had dimensions of 4 cm.×26.3 cm. withactive material of 4 cm.×25.3 cm. on one side and 4 cm.×20.3 cm. on theother side. The core was fabricated using copper foil. The firstseparator/binder was prepared by dissolving 0.5 gm of PVC in 20 gm ofTHF (tetrahydrofuran) then adding 9.5 gm of ball milled borosilicatefibers. After coating and drying the first separator/binder on bothsides of the cathode, both the cathode and uncoated anode were wound onthe core. The wound electrodes were then dipped in a liquid containing 1gm of PEO, 30 gm of methanol and 5 gm of ball milled borosilicate forabout 2 minutes. After removal from the liquid the assembly was dried ina vacuum oven at 120° C. for 12 hours. In a dry box, the electrolyte 1MLiPF₆ in EC/DMC wt. ratio 1:1 was added.

FIG. 27 graphically depicts the testing conditions. The battery wasfirst charged and discharged at a current of 0.15A. The battery was thencharged and discharged for 10 cycles with charging at a current of 0.3A(approximately C/1-in C-rate) with a constant voltage charge at 4.2volts, and a discharge current of 0.3A. The performance of the batteryis shown graphically in FIG. 28.

In a sixth example, the battery consisted of one anode and one cathodewound about a cylinder shaped core and fabricated by the third method offabrication. The cathode had dimensions of 3.8 cm.×24 cm. with activematerials of 3.8 cm.×23 cm. on one side and 3.8 cm.×21.7 cm. on theother side. The anode had dimensions of 4 cm.×24 cm. with activematerial of 4 cm.×23 cm. on one side and 4 cm.×19.2 cm. on the otherside. A glass fiber reinforced cylinder was used as the core.

The cathode was coated on both sides with a composition consisting of 1gm of PE/PP, 40 gm of TCE, and 5 gm of ball milled borosilicate fibers.The anode was coated on both sides with a composition consisting of 1 gmof PEO, 30 gm of methanol, and 5 gm of ball milled borosilicate fibers.After coating and drying the anode and cathode coatings, the anode andcathode were wound on the core. The assembly was then immersed in thesolvent of the second separator/binder, that is methanol, so as todissolve at least a surface layer of the second separator/binder. Theassembly was then dried in a vacuum oven at 120° C. for 12 hours. Afterdrying the assembly was transferred to a dry box where a liquidelectrolyte, 1M LiPF₆ in EC/DMC wt. ratio 1:1, was added.

The battery was cycled between 4.2 and 3.0 volts at a constant currentof 0.05A. The capacity versus cycle number for the first 20 cycles oftesting are shown in FIG. 29.

While specific material, dimensions, fabricating steps, etc. have beenset forth for purposes of describing embodiments of the invention,various modifications can be resorted to, in light of the aboveteachings, without departing from Applicants novel contributions;therefore in determining the scope of the present invention, referenceshall be made to the appended claims.

What is claimed is:
 1. A method of fabricating a rechargeable batteryhaving at least one anode, at least one cathode in opposing spacedrelationship with each anode, two layers of a porous separator/binderintermediate each opposed anode and cathode to maintain said spacing andto bind each anode to each cathode, and an non-aqueous electrolytefiling pores of each separator/binder, said method comprising coating atleast one surface of each said anode and/or cathode with a layer of afirst separator/binder containing polymer P₁ with polymer P₁ dissolvedin solvent S₁, in a manner such that a single layer of said firstseparator/binder is present between each anode and cathode in thebattery when fabrication is complete; then drying each said layer ofsaid first separator/binder; then providing a layer of a secondseparator/binder containing polymer P₂, with polymer P₂ at leastpartially dissolved in a solvent S₂, to at least one coated ornon-coated surface of each anode and/or cathode in a manner such that asingle layer of said second separator/binder is present between eachanode and cathode in the battery when fabrication is complete; placingeach anode in opposing spaced relationship to each cathode; then dryingeach layer of said second separator/binder so as to bind each said anodeto each said cathode; said first separator/binder comprising the polymerP₁ and a particulate material M₁, said second separator/bindercomprising the polymer P₂ and a particulate material M₂, wherein:polymer P₁ is soluble in solvent S₁, polymer P₂ is soluble in solventS₂, polymer P₁ is non-soluble in solvent S₂, polymer P₂ is non-solublein solvent S₁, particulate material M₁ is non-soluble in solvent P₁, andparticulate material M₂ is non-soluble in solvent S₂.
 2. A method offabricating a rechargeable battery according to claim 1, furthercomprising preparing the first separator/binder by dissolving polymer P₁in solvent S₁, adding particulate material M₁ to the solution, thenstirring the resulting mixture until the mixture is homogeneous, andpreparing the second separator/binder by dissolving polymer P₂ insolvent S₂, adding particulate material M₂ to the solution, thenstirring the resulting mixture until the mixture is homogeneous.
 3. Amethod of fabricating a rechargeable battery according to claim 1,wherein at least each first separator/binder layer is applied by a barcoating method.
 4. A method of fabricating a rechargeable batteryaccording to claim 1, wherein each said layer of second separator/binderhaving polymer P₂ dissolved in solvent S₂, is provided prior to placingeach anode in opposing spaced relationship to each cathode.
 5. A methodof fabricating a rechargeable battery according to claim 1, wherein eachanode is placed in opposing spaced relationship to each cathode prior toproviding the layer of second separator/binding, and polymer P₂ iscompletely dissolved in solvent S₂.
 6. A method of fabricating arechargeable battery according to claim 1, wherein each said layer ofsecond separator/binder, having polymer P₂ dissolved in solvent S₂, isprovided prior to placing each anode in opposing spaced relationship toeach cathode, and further comprising initially drying each layer of saidsecond separator/binder prior to placing each anode in opposing spacedrelationship to each cathode, and at least partially dissolving polymerP₂ of the second separator/binder with solvent S₂ following said placingeach anode in opposing spaced relationship to each cathode and prior tosaid drying each layer of said second separator/binder so as to bindsaid anode to each said cathode.
 7. A method of fabricating arechargeable battery according to claim 4, further comprising partiallydrying the second separator/binder until it is tacky prior to placingeach anode in opposing spaced relationship to each cathode.